Add mirror option

[cfcurtis]

Add the option to duplicate the stitched output on a second page in mirror view.

[mara004]

What would the transformation matrix look like for horizontal/vertical mirroring?

[cfcurtis]

Admittedly I haven't looked into it much because my new job is sucking up all my time right now, but I would probably start by trying to modify the Matrix property of the page xobject. For an X axis flip, I would try:

-1 0 0
 0 1 0
 0 0 1

which corresponds to [-1 0 0 1 0 0]. Similarly, for vertical I would try [1 0 0 -1 0 0]. However, there may also be some translation required, as I suspect this mapping would flip the content off the edge of the page.